The present invention relates to a multi-valve engine on which a plurality of intake or exhaust valves are mounted to a cylinder.
In such a multi-valve gasoline engine, DOHC-type valve-operating mechanism, two intake and exhaust valves are usually mounted on a cylinder.
The intake and exhaust valves used in such a multi-valve are made of the same material for an intake or exhaust valve depending on form and specification of the engine.
Recently, owing to intensification in regulation of a toxic exhaust gas and reduction in discharge amount of CO2, intake and exhaust conditions of a gasoline engine are inclined to vary widely. Various measures and changes in specifications are carried out. For example, to reduce NOx, a lot of EGR (exhaust gas recirculation) is carried out, or to increase fuel efficiency, swirling flow is formed in a conduit, or changing a phase of a camshaft. For example, internal EGR is conducted to reduce pumping loss to increase engine performance. The measures may especially affect an intake valve. To reduce NOx, a lot of EGR is made, and a high temperature gas passes through part or all of multi-valve provided intake valve to reflux into a cylinder to raise temperature of the intake valve.
To form a swirling flow in conduits, there is a method of stopping part of a multi-valve intake valve, but new air does not pass through a stopped intake valve, thereby decreasing cooling capability under the valve head to raise temperature.
Furthermore, to control new intake amount, internal EGR is carried out while multi-valve-type intake valve is partially stopped to raise temperature of stopped intake valve.
Measures for reducing toxic exhaust gas and increasing fuel efficiency increase thermal load of an intake valve to reduce heat resistance and accelerating wear. It becomes unreasonable in cost, reliability and engine performance to make a plurality of intake valves from the same material, since one intake valve becomes excessive quality to decrease durability.
In a multi-valve diesel engine, a plurality of intake valves are made of the same material, and a plurality of exhaust valves are made of the same material. In a diesel engine in which one exhaust valve is a little opened to actuate an exhaust brake, it involves disadvantages to make the valves of the same material.
In view of the foregoing disadvantages, it is an object of the present invention to provide a multi-valve engine which decreases its cost to increase durability, reliability and engine performance by determining material of a plurality of intake and exhaust valves respectively depending on intake and exhaust conditions and use of valve.